This invention relates to control systems for governing in situ removal of a hydrocarbon-based fluid from soil contaminated with the fluid and, in particular, for governing removal of the fluid by bio-remediation without endangering ground water supplies.
Relatively recently, environmental concerns over introduction of hydrocarbon-based fluids, such as solvents, gasoline, diesel fuel and oils for example, into the environment have escalated. This concern is primarily due to a better understanding of the detrimental effects that the hydrocarbon-based fluids have, both directly on botanical life and indirectly on animal life by contaminating ground water supplies, inter alia. Various methods for cleaning up sites contaminated with hydrocarbon-based fluids have been developed remedy the problem.
Current methods include removal of the soil to areas that are less affected by such contamination, in situ removal of the fluid from the subsurface, and bio-remediation. Problems with removal of the soil are readily apparent. There is great expense in removing and replacing soil which is often around or under an existing edifice. Further, dumping areas which are willing to accept contaminated soil continuously dwindle in number and increase in cost.
The practice of in situ removal of the fluid from the soil subsurface is a more recent development. Current methods include boring a well into the subsurface and either recovering a portion of the hydrocarbon-based fluids by skimming, or pumping groundwater out from below the hydrocarbon-based fluids to cause some portion of the hydrocarbon-based fluids to collect in previously uncontaminated regions and then pumping the hydrocarbon-based fluids out. Another method involves intercepting the hydrocarbon-based fluids in a trench or drain constructed at a level below the spilled fluid. These three methods are typically ineffective and cause further spread of the contaminants through the subsurface of the soil. Often they result in a portion of the hydrocarbon-based fluids remaining trapped in soil and groundwater.
Further, such problems are compounded in the case where the contamination is with a viscous hydrocarbon-based fluid. In this case, the first method could lead to isolation of the fluid from the well, rendering the well useless for further recovery of fluid from a contaminated zone. The second method induces the flow of fluid into the zone previously occupied by groundwater. This spreads the spilled fluid downward and establishes new equilibrium conditions in the region. While this permits some spilled fluid to be removed, additional removal requires the sequence be repeated so that the spilled fluid is driven to deeper and more extensive regions of the subsurface. A large volume of the spilled fluid will remain trapped as residual saturation in the new regions of contamination, significantly reducing the portion able to be recovered and requiring treatment of a large volume of contaminated water.
Bio-remediation is a more recent alternative. In bio-remediation, microbes are dispersed in a nutrient rich medium throughout the contaminated site. As the microbes penetrate subsurface due to gravity forces acting thereon, they consume the hydrocarbon-based fluid transforming the hydrocarbon-based fluids into an environmentally harmless by-product. A problem with bio-remediation is that the nutrient rich medium required for the microbes to thrive is itself hazardous to ground-water supplies.
To deal with this problem, an air pump is used to evacuate environmental gases and moisture from below the furthest depth of contamination. Drawing out the gases and the moisture creates a barrier to further penetration of the nutrient rich medium and microbes. This solution brings with it an additional problem. The air pump is left on twenty-four hours a day for weeks if not months. The air pump can not be turned off or else the barrier may be penetrated.
Therefore, what is needed is a method for the recovery of a spilled fluid which is capable of removing the spilled fluid from soil in situ, while at the same time preventing the spread of the spill.
Accordingly, it is an object of this invention to biologically remediate spilled hydrocarbon-based fluids from a site without contaminating groundwater.
It is another object of this invention to remediate spilled hydrocarbon-based fluids from a site without spreading the hydrocarbon-based fluids to other locations.
It is still another object of this invention to biologically remediate spilled hydrocarbon-based fluids from a site while conserving energy and lowering costs.
These and other objects of the invention will be obvious and appear hereinafter.